1. Field of Invention
The present invention relates generally to serial bus protocols and bus designs utilizing these protocols.
2. Description of Related Art
When separate devices or entities communicate, packets (the terms packet and frame are often used synonymously, but in this invention packets will generally refer to data payload while frames are used in the context of the invention) of data bits are transmitted in a series of blocks or units (frames), using a particular rule format, or protocol, such as when the entities are peers on the same layer, consisting of information bits that are parsed into components. The informational bits of the frame comprise both digital data that is sought to be transmitted (often simply called the “data”) as well as bits that are considered overhead required by the protocol (control field data bits). The latter overhead bits are sometimes called the header or trailer of the frame. The overhead bits not part of the informational bit data are sometimes called the “overhead tax” of the packet.
Over a traditional network (such as a Wide Area Network), various protocols or data communication standards exist for sending digital data, both synchronously, such as in synchronous time division multiplexing (TDM) networks, and asynchronously, such as in packet store-and-forward networks. These protocols are vital for increased throughput, efficiency, reduced error rate, scalability, traffic engineering, service differentiation, uniformity and other parameters measuring Quality of Service (QoS). These protocols can exist at any level of the traditional OSI model for networks, but typically are found in the data link layer (layer 2) or network layer (level 3). Protocols are implemented in hardware (e.g. an ASIC), software, or both, and typically involve sending packets (blocks of data transmitted as a single entity). The development of protocols has been the result of collective effort, often ratified by standards bodies like the ISO, ITU and ANSI, with QoS considerations at the forefront. Some protocols include, generally, (with numerous versions of each): ADCCP, AppleTalk, ATM, BGP, EGP, Ethernet, FDDI, frame relay, HDLC, IP, IGRP, IPX, ISDN, LLC, MPLS, MPOA, NetBIOS, OSPF, PPP, SDLC, SMDS, SONET, RIP, TCP/IP, Token Ring, VLAN, 802.1 and X.25.
Over a serial bus, such as communication between serdes (serializer/deserializer circuits), another type of protocol is to use a serial bus protocol that employs a eight-bit-to-ten-bit (8B/10B) encoder. This protocol is employed in order to guarantee that the resulting transmitted code has a minimum frequency of bit transitions (HIGH to LOW or vice versa), needed for clock recovery in serial bus implementations, as well as to provide DC balance. One of the aspects of the present invention is to realize that this conventional serial bus protocol is too restrictive and imposes too high of an overhead tax in certain situations where so-called DC balance is not important. Consequently, a new protocol and implementation of a serial/parallel bus employing this protocol is disclosed by the present invention.